Make braspag methods work asynchronously. Most meaningful changes are:

- Updated travis configuration
- Created requirements files
- Created Makefile to use nosetests with coverage
- Removed test with mock requests and responses -- which we'll eventually add back
- And, of course, changes to these methods to make them async: authorize, refund, void, capture, get_transaction_data, get_order_data, get_customer_data
- The above mentioned methods are now all class-based
- Docstrings of braspag/core.py updated
- Moved the mock data files to tests/data-unused, I think it's good to keep them in the tree so that we might reuse them if we can add mocked tests back in the near future